The future of microelectronic devices will depend on new designs and new materials having superior properties. Metals like cobalt, and compounds like cobalt silicide, are useful candidates for use in memory devices. Cobalt silicide (CoSi.sub.2) shows advantages over the currently used tungsten silicide (WSi.sub.2) due to its lower polycrystalline film resistivity (about 15 .mu..OMEGA.-cm for CoSi.sub.2 compared to about 70 .mu..OMEGA.-cm for WSi.sub.2). Furthermore, CoSi.sub.2 shows good thermal and chemical stability.
In some applications, metal films are deposited using sputtering techniques; however, sputtered metal is not typically effective at filling contacts or vias because of shoulders or overhangs that form at the contact openings. These overhangs can lead to the formation of keyhole-shaped voids. Various collimation techniques help reduce this problem, but typically not enough to enable complete filling of very small geometries (e.g., less than about 0.5 .mu.m). Therefore, it is desirable to use chemical vapor deposition (CVD) to form metal and metal alloy films.
The desirability of CVD processes depend on the availability of suitable precursor complexes. Many precursor complexes are unsuitable because of their toxicity, pyrophoricity, poor volatility, and thermal instability. Thus, there is a continuing need for methods and precursor complexes for the deposition of metal films (including metal alloy films), on semiconductor structures, particularly using vapor deposition processes.